gnomes are good because of the increased mana pool, but idk if that racial will stay that way with the plan to make mana pools consistently the same across the board. Humans are a good choice all around because you get bonus spirit (which will be a main mana regen tool in MoP) and a free trinket. HOWEVER, play the race that YOU want to play. If you are not concerned about playing a race that will be good for MoP, ignore my entire post

Favorite Owned Title: Champion of Ulduar
Favorite Owned Mount: Ashes of Al'ar
"Prisoners? Ha. With it bindings unshackled, its gonna' come after us, and we're going to be the prisoners" -- Brann Bronzebeard on Yogg'saron